1. Field of the Invention
The present invention is directed to a vibrating structure that may be manufactured in one piece by the techniques of a micro-machining. The vibrating structure has oscillating masses whose displacement indicates Coriolis forces of a capacitive rate gyro.
2. Description of the Related Art
A common application of vibrating structures of this kind is to act as a sensitive component for a capacitive rate gyro. They include two masses which vibrate in a common plane and a same direction, but in phase opposition, and which are connected by flexible beams or strips to a more rigid portion of the structure. Applying an alternating electric field between the masses and fixed portions of the structure adjacent to them causes the masses to oscillate. If the structure is subject to a rotational movement around an axis perpendicular to the direction of oscillation but belonging to the plane of oscillation, the Coriolis forces are expressed as displacements of the masses. The masses are displaced in a direction perpendicular to the axis of rotation, and at a distance proportionate to the speed of rotation in a direction perpendicular to the plane of oscillation. These displacements may be addressed if the masses and the adjacent and fixed portions of the structure, located in the direction of displacement, are constructed as a capacitor, since they may be correlated with variations in capacity, which can be easily measured.
One problem encountered with vibrating structures of this kind arises from machining inaccuracies, from unavoidable dissymmetries between the masses, from the influence of their attachment components, from the residual constraints which make it difficult to give them exactly the same inherent frequency, and to impose on them displacements which are exactly in phase opposition. It is for this reason that the document WO 96 39614 discloses a vibrating structure of this kind, wherein the masses are connected to each other by a coupling system including, on each side, a flexible arc-shaped beam and a beam parallel to the direction of oscillation, the ends of which are fixed to the rigid part of the structure and the middle of which is joined to the top of the arc-shaped beam. The oscillations produce distortions of these coupling beams, but movements in phase opposition produce a symmetrical distortion which, in respect of this particular embodiment, distorts the coupling beams in a more straightforward way and absorbing less energy than would be the case for displacements of the masses which are equal but in phase. The coupling system, more flexible in respect of displacements in phase opposition, therefore favours the latter.
Criticisms may be made of this design in respect of the dissymmetrical shape of the beams holding the masses, the sensitivity of the system to inaccuracies of machining causing dissymmetries between the masses, less freedom of choice for the geometries of the different beams of the proposed coupling system compared to the invention presented here. This design also imposes a way of fixing the device, by anchorages, which is not as favourable to the displacement of the masses under the Coriolis force as the example of the proposed invention makes possible, and is not therefore as favourable to a high sensitivity of measurement.
The present invention makes it possible to offer a better solution in these respects, and allows two oscillators to be coupled at the required phase difference.
In its most general form, the invention relates to a vibrating structure, including at least two oscillators vibrating in a direction of oscillation included in a plane, a rigid support of the oscillators and oscillator coupling means able to couple their vibratory movements, these means being connected, on the one hand to the rigid support and on the other hand to the oscillators, each oscillator comprising at least one mass and at least one flexible arm connecting the mass to the coupling means, characterised in that said coupling means comprise flexible attachment means connected to the rigid support and to at least one flexible arm of each oscillator by at least one point of attachment, making at said point of attachment a pivot.
To advantage, the coupling means are all or partly located within the rigid support.
In a preferred embodiment, the coupling means of two of the oscillators comprise at least one coupling unit formed by means of attaching each oscillator to the rigid support, and beams allowing the attachment means to be connected to the rigid support while providing a transfer of movement from at least one of the pivots of one oscillator to at least one of the pivots of the other of said two oscillators.
Frequently, the structure comprises two coupling units, each unit connecting symmetrically all the oscillators of the structure.
In a particular construction, the beams of the coupling means include at least two intermediate beams extending ends of the arms and a median beam connecting the intermediate beams to each other; it is then possible for the intermediate beams to be oblique to the median beam.